Heating element for cooking appliances

ABSTRACT

The invention relates to a heating element for a cooking appliance, particularly for the direct or indirect electrical heating of at least one item to be cooked, including at least one supporting layer, at least one heating element layer, which contacts the supporting layer at least in sections in a direct or indirect manner, and including at least one electric contact element or conductor element, with at least one elastic arresting element, which is or can be connected to the electric contact element or conductor element. The electric contact element or conductor element can be brought into contact, at least occasionally, with at least one heating resistor and/or with at least one contact point of the heating element layer via the elastic force of the elastic arresting element.

The present invention concerns a heating element for a cookingappliance, especially for direct and/or indirect heating of at least onecooking product, comprising at least one supporting layer and at leastone heating element layer which contact the supporting layer at least insections in a direct or indirect manner. Furthermore, the inventionconcerns a cooking appliance comprising at least one heating elementaccording to the invention, as well the invention.

Heating elements for cooking appliances have been known to the personskilled in the art for a long time. These are generally electricalheating systems or cooking fields for cooking appliances with anon-metallic, for example ceramic, or metallic supporting plate andheating resistors applied onto it directly or indirectly. For example,DE 40 28 354 A1 discloses a heating element comprising a supportingplate made of ceramic material with several conducting resistor pathsapplied on this supporting plate which in turn can be supplied withcurrent through control elements that are arranged on the back side.Bimetallic switches are proposed as control elements which, when aconducting contact is deviated sufficiently due to the heat, will createor interrupt the resistance or conducting paths. The connection of thebimetallic strips to the electric lines is conventionally done bysoldering or screw-in contacts, so that failure of the heating elementmay occur due to material stresses in the region of the contact causedby heat load and/or temperature fluctuations.

DE 100 06 953 A1 concerns electric hotplates containing at least oneheating element and a temperature sensor which is connected to a heatconducting element, which can be designed as an elastic element, and ispressed against the bottom side of the electric hotplate in the regionof the temperature sensor. In this way, through a permanent contact withthe hotplate, the temperature of it can be determined continuously andreliably. The contact to an electrical heating is produced through aheating conductor connecting part in the form of a plug contact attachedto the outer peripheral wall of the electric hotplate. The heatconductor connecting part is thereby connected, on the one hand, in aconductive manner with heat conductor bands, and, on the other hand,with electrical supply lines of the electric hotplate and thusthemselves are exposed to extreme heat radiation. Therefore, here too,erroneous functioning of the electric hotplates may occur when theelectric contact fails due to heat exposure and due to the materialstresses related to that.

DE 694 05 958 T2 discloses a steam generator with an electrically heatedplate, comprising a first fixed plate which is equipped with anelectrical heating resistor and a second mobile plate, which is pressedagainst a first main surface of the first plate by elastic devices. Herethe electrical heating resistor is guided through the inside of thefixed first hotplate. Since the heating resistor is incorporated intothe hotplate, it is no longer possible to control the electric hotplatethrough this heating resistor locally. Also, failure of a heatingresistor leads to a total failure of the steam generator.

DE 36 20 203 A1 describes an electric heating element consisting of aheating part and a connecting part, which consist at least partly ofdifferent electrically conducting materials, as a result of which theflexibility is increased and the mounting is supposed to be facilitated.In this way the heating part can be connected to the connecting part viaseparable clamping or plug connections in order to make such temporaryconnection possible without the use of an elastic element. Here, too,failure of the heating element may occur due to a defect in theelectrical energy supply.

Furthermore, from DE 197 01 640 A1 a contact heat transferring cookingsystem with an electric cooking plate with a cooking plate body isknown. The cooking plate body is heated through a heating resistanceapplied on its bottom side in the form of spiral or radial conductingbands. By designed control of the individual conducting bands orshort-circuiting of several conducting bands, multicircuit cookingplates are obtained consisting of several heating zones. In order toachieve different heat outputs in various regions of the electrichotplate body, the conducting bands in the individual heating zones arecontrolled separately from one another. This increases the expenditurefor the circuits and makes the use of several sensors necessary in thevarious regions of the electric hotplate to control a uniform heatingoutput. This makes the electric hotplate require very high maintenance.

Modern electric hotplates or heating areas are characterized by the factthat a number of locally-limited heating elements can be controlled in adesigned manner. Again, individual heating elements may have one orseveral heating resistors. The smaller the particular heating elementunits or heating resistor units and the more densely they are provided,the higher the expenditure for the technology of the apparatus requiredto control or regulate each individual heating resistor separately,which leads to increased failure probability. Ideally, each individualheating resistor is connected through a separate electrical line to acontrol and regulating unit. The connection of the heating resistors tothe electrical lines usually occurs through soldered contacts. In anycase, the production of these is labor-intensive and time-consuming andalso very expensive with regard to materials and thus overall it is acost-driving factor. In addition, these soldered connections arecontinuously exposed to very high temperatures and significanttemperature fluctuations, and therefore usually rapid material fatigueespecially in continuous operation must be accepted, especially in largekitchens or cafeterias. The requirements related to this often lead to anegative evaluation of the value of the cooking appliance used sincerepairs frequently can be performed only by experts and this is relatedto lost time as well as to repair costs which are not negligible. Inaddition, non-uniform pressing pressure of a heating element to asurface to be heated leads to a different heat input at different pointsof the surface and thus to defective cooking results.

Therefore, the task of the present invention was to develop the genericheating elements for a cooking appliance in such a way that it does nothave the disadvantages of the state of the art and especially itprovides electric hotplates with a high density of heating resistanceswhich are very maintenance- and operator-friendly. Mainly, a heatingelement should be provided which makes it possible to have a verymaintenance-friendly control and uniform and failure-safe introductionof heat into a carrier layer, especially into a pan of a cookingappliance. Furthermore, a cooking appliance as well as a method forproduction of a heating element layer of a heating element are to beprovided which overcome the disadvantages of the state of the art.

Accordingly, a heating element was discovered for a cooking appliance,especially for direct or indirect electrical heating of at least onecooking product, having at least one supporting layer, at least oneheating element layer which lies directly or indirectly against thesupporting layer at least in sections, and with at least one electricalcontact or conducting element and with at least one elastic arrestingelement which is or can be connected to the electrical contact orconducting element, whereby the electrical contact or conducting elementcan be brought into contact through the elastic force of the elasticarresting element at least intermittently, with at least one heatingresistor and/or with at least one contact location of the heatingelement layer.

With the heating element according to the invention it is possible toconnect hotplates, heating layers or heating resistors without anysoldered contact to an electric conductor band reliably and permanentlyand thus almost free from maintenance. For this purpose generally it isonly required that the conducting element be pressed through the elasticforce of the arresting element, for example a spring, to the heatingresistor or be clamped between the arresting element and the heatingresistor. For example, the conductor element, in an expedient embodimentof the invention, can be designed to be rigid and in addition connectedin a fixed manner to the elastic arresting element. In this case, theelastic force of the arresting element is chosen appropriately in such away that the conductor element is surely pressed on the heatingresistor, but its shape is not thereby altered permanently.

Hereby, in another embodiment it can be provided that this heatingelement be a hotplate, especially an essentially flat heating plate orby heating that is completely or in regions essentially tubular,especially in a cylindrical form. Accordingly, the heating elementsaccording to the invention are especially suitable for use in rotaryevaporators, as they are described, for example, in WO 02/12790 as steamgenerators for cooking devices. The heating plates can be fundamentallyflat, bent, wavy or have any other desirable form.

In a further expedient embodiment of the invention, at least in sectionsat least one separating layer is present between the supporting layerand the heating element layer, preferably comprising at least onegraphite layer for making the heat input into the supporting layer atleast partially uniform at least in regions, and/or having at least onemechanical buffer layer, preferably including a mica layer and/or atleast one first thermal insulating layer present at least in sections onthe side of the heat element layer which is away from the supportinglayer and/or between the heating element layer and the elastic arrestingelement. In one embodiment, the supporting layer can be designed as acarrier plate. Naturally, for example, the supporting layer, the heatingelement layer, the separating layer, the mechanical buffer layer, thefirst thermal insulating layer and/or the elastic arresting element canbe adjusted to the selected form of the heating element or may assume itcompletely.

Hereby, according to an embodiment, it can be provided that thesupporting layer consist completely or partially of stainless steeland/or the mechanical buffer layer consist completely or partially ofmica.

According to a further aspect of the present invention, the heatingelement according to the invention comprises at least one pressingmeans, preferably comprising a pressing plate, with which the elasticarresting element preferably comprising an elastic element plate, themechanical buffer layer, the first thermal insulating layer, the heatingelement layer and/or the separating layer, can be pressed or is/arepressed against the supporting layer in order to make the pressingstrength onto the supporting layer and/or the heat input into thesupporting layer more uniform, at least in regions. The heating elementpresent in this embodiment has essentially a pressed sandwich structure.Because of the use of a mechanical buffer layer, for example in the formof a mica layer or the first insulating layer, preferably in the form ofa mica layer, both the arresting element as well as the heating elementlayer and/or the separating element layer or the graphite layer isprotected against mechanical overstressing or damage even during strongthermal exposure. This pressed-together structure is also space-savingfor storage and transportation and can be incorporated into cookingappliances in a simple and reliable manner.

According to an especially preferred further development, it should benoted that the mechanical buffer layer, the first thermal insulatinglayer and/or the pressing means have at least one outlet for the contactor conducting element in the region of at least one second section ofthe elastic arresting element. Since the mechanical buffer layer, thefirst thermal insulating layer, and the pressing means, between whichthe elastic arresting element is present, forced in, at least insections, have outlets, a second section of the arresting element hasfreedom of movement in the direction of the supporting layer and isremoved from this. For example, if the arresting element is a metalplate, this is usually stress-free in the planar, flat state. Bydeflecting at least a first section of the arresting element from thestress-free resting position, generally a restoring force is built up.The resulting restoring force can be used in the present case forpressing the conducting element connected to the deflected section ofthe arresting element or a contact element against the heating elementlayer.

Hereby, according to the invention, it can be provided that the elasticarresting element have at least one first section, lying, on the onehand, between the heating element layer, the first thermal insulatinglayer and/or the mechanical buffer layer, and, on the other hand, thepressing means, and a second free section which is connecting the firstsection, the second free section being able to be connected directly orindirectly to the contact or conducting element, especially through athird section, whereby the second free section preferably lies in thesecond region of the outlet. Accordingly, the arresting element has atleast one first section, which is clamped between the pressing means andthe supporting layer, preferably the mica layer, and a second section,which can essentially be freely swiveled. Hereby the conducting elementcan be connected directly to this second section or it can be connectedby inserting another, third section with the arresting element. In oneembodiment, the arresting element ends with its free end, that is, thefirst or third section in the region of the conducting element.

In any case, according to a further embodiment, at least one fourthsection can be provided which is attached to the second and/or thirdsection of the elastic arresting element and/or to the contact orconducting element, whereby the fourth section is preferably connectedor can be connected to the mechanical buffer layer, the first thermalinsulating layer and/or to the pressing means. For example, the fourthsection can be used to support the arresting element at the edge of theoutlet, and which lies opposite the first section of this. In this waythe room for movement of the arresting element is limited, but not tosuch an extent that it could prevent bonding with the aid of elasticforce. Rather, with the aid of the fourth section, a very safepositioning of the arresting element can be achieved.

More preferably, the contact element or conducting element can beconnected through an insulator, preferably in the form of an insulatingsleeve, to the elastic arresting element, especially to the second,third and fourth sections thereof. For example, this can be aninsulating sleeve which is inserted on the one hand into the second orthird section of the arresting element and on the other hand can holdthe contact element so that it can be shifted.

Especially advantageous heating elements are characterized by the factthat the heating element according to the invention, looking from thesupporting layer in the direction of the elastic arresting element, assupporting layer or as heating element layer at least in sections atleast one stainless steel layer and/or at least in sections at least oneceramic layer as well as furthermore at least in sections at least onelayer with electrical heating resistors and/or at least in sections atleast one glass layer. Naturally, the glass layer is not continuous atthe positions at which the conducting element comes into contact withthe heating resistor.

According to an alternative embodiment, a supporting layer according tothe invention is used, which, viewed from the free outside surface ofit, has at least one layer containing at least one heat conductingmetal, especially steel, at least one layer containing at least onemetal with good thermal conductivity, especially copper, and at leastone second insulating layer.

Furthermore, alternatively, it can be provided that the supportinglayer, viewed from the free outside surface, has at least one layercontaining at least one metal with good thermal conductivity, especiallycopper, at least one layer containing at least one metal with poorthermal conductivity, especially steel, and at least one secondinsulating layer.

Furthermore, those heating elements according to the invention are alsosuitable in which the supporting layer, viewed from the free outsidesurface, has at least one electrically insulating ceramic layer, atleast one electrically conducting ceramic layer and/or at least onesecond insulating layer.

Hereby it can be provided that the heating element layer is designed asa thick film or as a thin film.

Hereby it can be provided that the heating element layer can be producedby serigraphy or by a printing process, for example as a thick film.

Furthermore, the task on which the invention is based is solved inanother embodiment by a heating element in which the heating elementlayer has a plurality of individual heating resistors, which arearranged in at least two heating tracks in such a way that the heatingresistors within each heating track are electrically connected parallelto one another, and the heating tracks are connected to one anotherelectrically in series and that all heating resistors can be suppliedsimultaneously with electrical energy, whereby at least two differentheating resistors have different heating powers and/or the heatingresistors are arranged on the heating element layer at differentdistances to one another, at least in regions.

The invention can also be characterized by the fact that the heatingresistors are provided through a thick film.

Furthermore, it can be hereby provided that the heating resistors on theheating element layer can be produced with serigraphy or a printingprocess.

Furthermore, it is proposed with the invention that at least two heatingresistors have different electrical resistors with different heatingpowers, especially different geometrical dimensions and/or are made ofdifferent materials, especially materials with different dopings.

Hereby it is preferably provided that the at least two heating resistorswith different surface areas have different peripheral shapes,especially at least one heating resistor has an essentially polygonalshape, especially trapezoidal, triangular, square, rectangular and/orhexagonal peripheral shape, different peripheral lengths, different sidelengths, especially different widths and/or lengths, and/or differentthicknesses.

Another further preferred embodiment of the invention provides that theheating power and/or the distance of the heating resistors, at least inregions preferably over the complete heating element, be adjusted to apressing strength of the heating element layer on the supporting layerpresent at least in regions, to a predetermined heating power densitydistribution within the heating element layer which is present at leastin regions especially as a function of a local thermal conductivity ofthe supporting layer, and/or to a predetermined heat densitydistribution within the supporting layer, at least in regions.

In addition, it is hereby provided that the heating power of a firstheating resistor which is arranged in a first region of the heatingelement layer with a first pressing strength of the heating elementlayer onto the supporting layer, is smaller than the heating power of atleast one second heating resistor, which is arranged in a second regionwith a second pressing strength that is smaller in comparison to thefirst pressing strength of the heating element layer to the supportinglayer and/or the distance of the two heating resistors to one another islarger in the first region than the distance between two heatingresistors to one another in the second region.

Furthermore, the invention provides that the first region be locatednear at least one preferably bordering at least one attachment locationor pressing location, preferably in the form of an opening for at leastpartial leadthrough or penetration of an attachment device for applyingthe heating element layer to the supporting layer, and/or the secondregion is located further removed in comparison to the first region fromat least one, especially not bordering on at least one attachmentlocation or pressing location.

Furthermore, it is preferred that the heating power of a third heatingresistor which is located in a third region of the heating element layerwith a first heating power density of the heating element layer besmaller than the heating power of at least one fourth heating resistorwhich is located in a fourth region with a second heating power densityof the heating element layer, which is smaller in comparison to thefirst heating power density, and/or the distance of the two thirdheating resistors in the third region is larger than the distance of thetwo fourth heating resistors in the fourth region.

Hereby it can also be provided that the third region of the heatingelement layer be located near at least one, preferably bordering atleast one, first region of the supporting layer with a first thermalconductivity and/or with a first heat density and that the fourth regionof the heating element layer is located near at least one, preferablybordering at least one, second region of the supporting layer with asecond thermal conductivity which is smaller in comparison to the firstthermal conductivity and/or with a heat density which is larger incomparison to the first heat density.

Furthermore, according to the invention it is proposed that theelectrical heating resistors of a heating track have essentially thesame heating power, essentially the same geometrical dimensions, areessentially at the same distance from one another and/or be madeessentially of the same materials.

Especially it can be provided that the separating layer, the heatingelement layer, the mechanical buffer layer, the first thermal insulatinglayer, the elastic arresting element and/or the pressing means aredesigned as one element.

Especially, it can be preferred according to the invention that thepressing means, the elastic arresting element, the mechanical bufferlayer, the first thermal insulating layer, the heating element layerand/or the separating layer can be joined to one another separably or ina fixed manner, especially with the aid of adhesion, preferably with theaid of an adhesive.

In one advantageous embodiment of the invention it is provided that eachof the heating tracks have a large number of heating resistors arrangedat least pairwise neighboring each other, whereby the heating resistorshave a surface that is limited at least partially, preferably in a planethrough first and second side edges, whereby two neighboring heatingresistors, for the purpose of achieving electrical parallel circuits,have first facing neighboring side edges, which are at least partiallyat a distance from one another, and/or especially are electricallyinsulated through at least one insulating intermediate layer orelectrical insulation.

Hereby it is proposed according to the invention that two facingneighboring second side edges of the heating resistors of neighboringfirst and second heating tracks, for the purpose of achieving electricalseries connection of the heating tracks at least partially, at least onefirst electrically conducting means, especially in the form of at leastone first electrical conducting path which lies especially at eachsecond side edge of the heating resistors of the first heating track andagainst, especially against each, second side edges of the heatingresistors of the second heating track, and can be connected to oneanother or are connected to one another, whereby with the aid of thefirst electrically conducting means an electrical current can beconducted through the electrical heating resistors of neighboring firstand second heating tracks.

Hereby it is preferred that at least one second electrically conductingmeans which connects at least two, especially all, second side edges ofheating resistors of an outer heating track to one another in aconducting manner, which are especially not neighboring a first orsecond side edge of a heating resistor, whereby the at least one secondelectrically conducting means has especially at least one contactposition and/or is in working relationship with at least one contactposition.

According to the invention it can also be provided that at least onethird electrically conducting means has especially no insulatingintermediate layer to at least one especially each first and/or secondside edge of a heating resistor of at least one first outer heatingtrack which is especially not neighboring a first or second side edge ofa heating resistor of a first or second heating track.

It is also proposed that the first, second and/or third electricallyconducting means have at least one electrical material of highconductivity, especially silver or copper.

Furthermore, it can be provided that the neighboring heating tracks bearranged essentially parallel to one another and/or at least one heatingtrack be arranged along a straight, curved or circular path.

It is especially preferred according to the invention that the heatingtracks be provided with different dimensions.

Finally, it can be provided in the heating element according to theinvention hat each heating track have at least three, especially atleast five, electrical heating resistors, and/or at least three,especially at least five, heating tracks, which are preferablyelectrically connectable through at least one first electricallyconducting means and/or through at least two contact positions, to apower source.

Furthermore, the invention provides a cooking appliance comprising atleast one heating element according to the invention.

This cooking appliance can be especially characterized by the fact thatat least one heating element, preferably all heating elements can besecured on the cooking appliance separably, especially through a screwconnection.

It is also proposed with the invention that a control and/or regulatingunit be provided which is in working relationship with at least one,especially with all, heating element(s) and/or with at least one,especially all, electrical heating resistor(s) and/or with at least onesensor.

Furthermore, it is proposed that, through the control and/or regulatingunit the heating power of the heating element, preferably of theindividual heating resistors and/or at least of two groups of heatingresistors can be regulated and/or controlled, especially as a functionof at least one characteristic quantity which can preferably be detectedwith the sensor, such as a temperature, a moisture content, a degree ofbrowning of the cooking product, a weight of the cooking product, a sizeof the cooking product, a type of cooking product or similar.

Finally, the invention provides a method for the production of a heatingelement layer of a heating element according to the invention comprisingthe steps of

-   preparing a substrate and-   applying heating resistors and/or electrical conducting paths with a    serigraphic technique.

Hereby it can be provided that subsequently at least one covering layeris applied at least in regions.

According to the invention it is preferred that the substrate be made ofat least one electrically conducting material, preferably a metal,especially stainless steel, glass, ceramic and/or a plastic, and/orbefore applying the heating resistors, at least one thermally- and/orelectrically insulating layer be applied onto the substrate at least inregions.

Furthermore it can be provided that the thermally- and/or electricallyinsulating layer be made with at least one ceramic material and/or atleast one glass.

Furthermore, it can be provided that the covering layer be made of anelectrically insulating material and/or a material protecting againstmechanical influences, preferably made of a glass and/or a protectivevarnish.

Finally, it is proposed with the invention that the heating power, theelectrical resistance and/or the distance of the heating resistors fromone another be adjusted by dimensioning the geometrical measurements ofthe heating resistors.

With the heating elements of the present invention, a durable reliablecontact between an electrical inlet and a heating resistor can becreated simply and this connection is not material-intensive orrequiring much repair. Moreover, in case of damage the defect can beeliminated rapidly and professionally even by a layman. Furthermore itis possible to provide and separately control a very large density ofindividual resistor units in a cooking field.

The maintenance friendliness of the heating element according to theinvention is increased even further in a claimed embodiment in that itmakes it possible to omit separate control of the individual resistorunits with a simultaneously high uniformity of the heat input. In thisembodiment with the aid of different sizes and the number of heatingresistors on a heating element, it becomes possible not only to reachhigh safety against failure but also to adjust the heating power of thedifferent regions of a heating element layer in a designed manner. Thus,for example, uniform heat input into a supporting layer is possible inspite of different pressing strengths of a heating element layer on thesupporting layer. For this purpose the heating powers of the individualheating resistors or the distance between the individual heatingresistors is adapted to the special environmental conditions in theindividual regions of the heating element layer or of the supportinglayer, for example the pressing strength of the heating element layeronto the supporting layer, to the thermal conductivity of the heatinglayer in different regions, etc. Furthermore, the life of the heatingelement layer is significantly increased since the failure of anindividual heating resistor is not harmful to the providing of uniformheat input into the supporting layer, due to the number of heatingresistors and because this failure can be compensated by neighboringheating resistors. Especially this is supported by the arrangement of aseparating layer between the heating element layer and the supportinglayer, since this leads to making the heat input more uniform.Furthermore, flow of current through the heating element is notprevented by the failure of one or several heating resistors. Thus, adesired cooking result can be achieved in spite of a failed heatingresistor.

Further characteristics and advantages of the invention follow from thedescription given below, in which a practical example of the inventionis explained in detail with the aid of a schematic drawing. Thefollowing are shown:

FIG. 1: a partial section of a heating element according to theinvention; and

FIG. 2: a top view of a heating element layer of the heating elementaccording to the invention according to FIG. 1.

FIG. 1 shows a heating element 1 according to the invention in a partialcross-section. According to a preferred embodiment, between a carrierlayer or plate 2 and a pressing plate 4 the following are arranged, inthis sequence: a separating layer in the form of a graphite film 6, aheating element layer 8, a mechanical buffer layer in the form of a micalayer 10 and an elastic element plate 12. The graphite film 6 is appliedon the bottom side of carrier layer 2 in a manner known to the personskilled in the art, especially to make the heat input into the carrierlayer uniform. The heating element or heating resistor layer 8 can beapplied, for example, with the aid of the known silk-screening method ina desired pattern, for example, onto graphite film 6. For the purpose ofmechanical protection of this resistance layer or heating element layer,it is covered by a mica plate 10 at least in the essential parts. On theside of the mica plate 10 away from the heating element layer 8, anelastic element 12 is arranged at least in sections. For example, thiscan be a metal plate which is equipped with elastic properties at leastin regions. The layer sequence of graphite film 6, heating element layer8, mica layer 10 and elastic plate 12 is held as tightly as possible onthe bottom side of supporting layer 2 using pressing plate 4. This canbe done, for example, with the aid of a screw-nut construction 14,especially in such a way that the screw or a continuation of the screwis rigidly connected to the bottom side of carrier layer 2 and with theaid of the nut 16 a pressing pressure is applied on the outside ofpressing plate 4, preferably by inserting a planar washer 18. Bysuitable adjustment of the nut 16 optimum pressing pressure can beachieved without fear of damage to the layer structure. In the region ofthe elastic element 12, as well as in the mica layer 10, an outlet 22 aswell as in pressing plate 4 an outlet 30 are provided so that a contactelement 24 to which the elastic element 12 functioning as the elasticarresting unit is connected is always in conducting contact with theheating element layer 8. If the elastic element 12 is made of metal, itis appropriate to connect the electrical line or the electrical contactelement 24 to the elastic element 12 not directly, but with intermediateswitching of an insulating sleeve 20. The contact element 24 ispreferably equipped rigidly with the heating element layer 8 in theregion of its contact, preferably with a strength which is sufficient towithstand a restoring force by the elastic element 12 without bending,even under thermal exposure. For example, copper rods were found to besuitable materials for these contact elements 24. The elastic element 12is squeezed between the pressing plate 4 and the mica layer 10 at leastthrough one section, essentially so that it cannot move. In the regionof outlet 22 we then have the possibility to bend out at least onefurther section 28 of the elastic element 12 in a direction away fromthe bottom side of supporting layer 2. Due to the elastic nature ofelement 12, there is always a restoring force acting on the contactelement 24 arrested in the insulating sleeve 20. This is utilized toprovide long-lasting and reliable contact with the heating element layer8. The outlets 22, 30 in mica layer 10 and in pressing plate 4 can bedimensioned differently in each case, but they can also have the samesize. Preferably the outlet 30 of the pressing plate 4 is larger thanthe outlet 22 of mica plate 10. Fundamentally, however, a reversedimensioning is also possible. Preferably, the elastic element 12extends beyond the insulating sleeve 20, for example with a section 34,and it can be designed in such a way that it will be in the region ofthe top side of pressing plate 4, with which it will be constructed.Since also in this section 34 of the elastic element 12, whose deviationaway from the bottom side of carrier layer 2 is utilized in a designedmanner in order to provide bonding of the contact element 24 ontoheating layer element 8, an especially safe and reliable contact sourceto an electrical line which is at least partly a component of contactelement 24 or to a power source is provided. Specifically, no solderedconnection of the electrical line to the heating element 1 is needed,but rather it is possible to omit soldered connections completely or toplace these into a region which is not exposed to any thermal ormechanical stress. The electrical contact element 24 which is present inan insulating sleeve 20, can also be replaced in case of damage withoutany problems. The same also applies to the entire elastic element 12when the pressing plate 4 is held with the aid of a screw construction14.

The heating element layer 8, the graphite film 6, the mica layer 10, theelastic plate 12 and the pressing plate 4 can also be separable orjoined to one another rigidly to simplify mounting, for example, using aglue. Furthermore, also various functions of the layers can be achievedwith a single component or a single layer, since essentially we aredealing with the function of a layer especially for making the heatinput uniform (separation and/or graphite layer) or for making thepressing pressure uniform (pressing and/or elastic element plate). Forexample, the pressing plate 4, which serves for pressing the variouslayers, and the elastic plate 12, which is installed for providingelastic pressing of the electrical contact element 24, can be made inone piece. Also, the mica layer 10 can fulfill not only the task of amechanical buffer layer but also the task of a heat insulating layer.Alternatively to that, especially bordering the heating element layer 8,an additional first thermal insulation layer can be provided, which ispreferably a mica layer.

Furthermore, the pressing plate can be made elastic at least on thesurface which is facing the heating element layer, so that the micalayer 10 can be omitted.

FIG. 2 shows a heating element layer 8 in a top view. Accordingly, theheating element layer 8 has heating tracks 804, 804′, 805, 805′ whichrun essentially straight and parallel to one another, and these tracksare composed of a plurality of electrical heating resistances 806, 807,806′, 807′. The electrical heating resistors 806, 806′, 807, 807′ have arectangular or square surface shape and in the present case are within aheating track 804, 804′, 805, 805′, which in each case have the samesurface area and shape. Within each heating track 804, 804′, 805, 805′,are neighboring electrical heating resistors 806, 807, 806′, 807′,always separated from one another by electrical insulation 812. Theinsulation 812 prevents direct contact of first side edges 810, namelythe first side edges 810.1 and 810.2 and 810.1′ and 810.2′,respectively, of neighboring heating resistors in the heating track. Incontrast to the first side edges 810.1 and 810.2 and 810.1′ and 810.2′,the second side edges 820 of neighboring heating resistors of a heatingtrack are not assigned to one another or are neighboring over longersections. Neighboring heating tracks, for example 804, 804′ and 805,805′ are not in direct contact with one another, but rather are joinedtogether through first electrical conducting paths 808. Hereby, thesecond side edges 820 of electrical heating resistors 806, 807, 806′,807′ of a heating track 804, 804′, 805, 805′ lie regularly against afirst electrical conducting path 808. Similarly, the second side edges820 of heating resistors 806, 807 of the always outer heating tracks804, 805 of the heating element layer 8 forming the outsides 817 and 819are connected to a second electrical conducting path 814 and 816. Inthis embodiment of a heating element layer according to the invention,electrical current cannot be conducted directly through neighboringelectrical heating resistors 806, 807, 806′, 807′ within a heating track804, 804′, 805, 805′. Rather the electrical current is conducted throughan electrical heating resistor 806 of a first heating track 804 by meansof a first electrical conducting path 808 to the electrical heatingresistor 806′ of a neighboring heating track 804′. For example, apossible pathway for the electrical current is shown in the depiction ofheating element layer 8 in FIG. 2 and is designated with A. For example,if an electrical heating resistor 806 within a heating track 804 wouldfail during operation, the large number of heating resistors and therelated relatively low surface area of the heating resistors connectedto it leads to the fact that the entire heating plate can be usedfurther without any problem. Especially, the failure of individualheating resistors 806, 807, 806′, 807′ can be compensated simply by theother electrical heating resistors 806, 807, 806′, 807′ of heatingtracks 804, 804′, 805, 805′, so that orderly operation of the cookingappliance can be maintained. In this way it is possible to react veryflexibly to the failure of individual electrical heating resistors. Thedesired cooking result is thus achieved even in the case of a partiallydamaged or not completely functional heating element layer 8. Thus,overall, the cooking appliance will have a heating plate with asignificantly longer effective life and thus lower maintenancerequirements.

In addition, it can easily be seen from FIG. 2 that the individualheating resistors in the different heating tracks occupy differentsurface areas. Thus, the individual heating resistors also havedifferent electrical resistances and thus different heat outputs. Thedifferent sizes of the heating resistors 806, 807, 806′, 807′ aresupposed to achieve especially equalization of the different heattransfer from the heating element layer 8 to the medium to be heated,especially to the supporting layer 2, see FIG. 1, which, for example,can occur due to a different pressing strength of the heating elementlayer 8 onto supporting layer 2 in different regions of the heatingelement layer 8 of the heating element 1 according to the invention. Forexample, the surface of the heating resistors in the regions around thefirst openings 822, 824, 826, 828, which represent the recesses for thescrew connection 14, are larger in order to compensate for the improvedthermal conductivity in the heat carrier layer 2 due to the largerpressing strength. Due to the larger surface of the heating resistorsand thus to their lower electrical resistances in this region, theheating power will be lower. Thus, the heating element layer 8 isdesigned so that the surface of the heating resistors is the largest inthe areas with the largest pressing pressure, that is, the lowestheating power will be provided by the heating resistors, and will becomesmaller the farther the heating resistor is removed from the firstopenings 822, 824, 826, 828. The heating power of these heatingresistors which are farthest removed from the first openings 822, 824,826, 828 is in fact larger due to the higher electrical resistance. Thusit is achieved that the heating element layer 8 makes it possible tohave a very uniform heat input over the surface into the supportinglayer 2 and thus, for example, into a cooking container. The electricalcontact elements 24 shown in FIG. 1 are most preferably located at thecontact points 830 and 830′ shown in FIG. 2, which are always connectedto a second electrical conducting path 814, 816 onto which heatingelement layer 8 is pressed. A second opening 832 is located in themiddle of heating element layer 8, which is provided for a heat sensor(not shown) and has essentially no influence on the pressing pressure.As a result of this design, monitoring of the heating power of heatingelement 1 is possible.

Thus, a plurality of heating elements 1 according to the invention,which always have a heating element layer 8, can be introduced separablyinto a cooking appliance, whereby the heating elements 1 or theirheating element layers 8 can have different sizes which are thenintroduced as a mosaic. Such a heating element layer 8 can be producedin the method according to the invention using a serigraphic techniqueor a printing technique, in a simple and uncomplicated manner. Hereby, aceramic layer is applied onto a substrate, preferably in the form of astainless steel plate, and onto that again heating resistors are appliedwith the serigraphic technique which can have different sizes in themanner described above and conducting paths can be printed onto it.Finally, a mechanical protection in the form of a glass layer can beapplied. This leads to very simple manufacture and the resistors can bedesigned arbitrarily on a model form.

Cooking appliances for which the heating elements according to theinvention can be used include especially pans, hot air cookingappliances, steam cooking appliances, combination steamers for operationwith hot air and steam, steam generators, heating devices in the form ofat least one cooking field and units for keeping food warm.

The characteristics of the invention disclosed in the abovespecification, the claims as well as in the drawings can be essentialfor realizing the invention in its different embodiments in anyarbitrary combination.

Reference list

-   1 Heating element-   2 Supporting layer-   4 Pressing plate-   6 Graphite film-   8 Heating element layer-   10 Mica layer-   12 Elastic element plate-   14 Screw construction-   16 Nut-   18 Plane washer-   20 Insulating sleeve-   22 Outlet-   24 Contact element-   26 Section of elastic element 12-   28 Section of elastic element 12-   30 Outlet in pressing plate 4-   32 Outlet in mica plate 10-   34 Section of elastic element 12-   804, 804′ Heating track-   805, 805′ Heating track-   806, 806′ Electrical heating resistor-   807, 807′ Electrical heating resistor-   808 Electrical conducting path-   810 First side edges-   810.1, 810.2 Neighboring first side edges-   810.1′, 810.2′ Neighboring first side edges-   812 Electrical insulation-   814 Outer electrical conducting path-   816 Outer electrical conducting path-   817 Outside of an outer heating track 804-   819 Outside of an outer heating track 805-   820 Second side edges-   820.1, 820.2 Neighboring second side edges-   824, 826, 828 Opening-   830, 830′ Contact point-   830 Opening

1. Heating element for a cooking appliance, especially for direct orindirect electrical heating of at least one cooking product, comprising:at least one supporting layer, at least one heating element layer whichlies directly or indirectly against the supporting layer at least insections, at least one electrical contact or conducting element, and atleast one elastic arresting element, which is connected or can beconnected to the electrical contact or conducting element, whereby theelectrical contact or conducting element can be brought into contact,using the elastic force of the elastic arresting element with at leastone heating resistor and/or with at least one contact location of theheating element layer.
 2. Heating element according to claim 1, whereinthe heating element comprises an essentially flat heating plate or adevice in which heating is completely or in regions essentially tubular.3. Heating element according to claim 1, wherein at least one separatinglayer is disposed between the supporting layer and the heating elementlayer at least in sections to make the heat input into the supportinglayer at least partially uniform, and/or at least one mechanical bufferlayer and/or at least a first thermal insulating layer is disposed onthe side of the heating element layer, which is away from the supportinglayer and/or between the heating element layer and the elastic arrestingelement, at least in sections.
 4. Heating element according to claim 3,further including at least one pressing means with which the elasticarresting element, the mechanical buffer layer, the first thermalinsulating layer, the heating element layer and/or the separating layer,can be pressed or is/are pressed against the supporting layer for makingthe pressing strength onto the supporting layer and/or of the heat inputinto the supporting layer uniform at least in regions.
 5. Heatingelement according to claim 4, wherein the mechanical buffer layer, thefirst thermal insulating layer and/or the pressing means has/have atleast one outlet for the contact or conducting element in the region ofat least one second section of the elastic arresting element.
 6. Heatingelement according to claim 5, wherein the elastic arresting element hasat least one first section which is between, on the one hand, theheating element layer, the first thermal insulating layer and/or themechanical buffer layer and, on the other hand, the pressing means, anda second free section, which is connected to the first section, the freesection being able to be connected directly or indirectly to the contactor contacting element.
 7. Heating element according to claim 6, furtherincluding one fourth section which is attached to the second and/orthird section of the elastic arresting element and/or the contact orconducting element, whereby the fourth section is preferably connectedor can be connected to the mechanical buffer layer, the first thermalinsulating layer and/or the pressing means.
 8. Heating element accordingto claim 7, wherein the contact or conducting element can be connectedthrough an insulator to the elastic arresting element.
 9. Heatingelement according to claim 3, wherein the supporting layer is madecompletely or partially of stainless steel and/or the mechanical bufferlayer is made completely or partially of mica.
 10. Heating elementaccording to claim 1, wherein looking from the supporting layer in thedirection of the elastic arresting element, the supporting layer or theheating element layer is defined, at least in sections, by at least onestainless steel layer and/or, at least in sections, by at least oneceramic layer as well as furthermore at least in sections at least onelayer with electrical heating resistors and/or at least in sections atleast one glass layer is disposed.
 11. Heating element according toclaim 1, wherein the supporting layer, viewed from a free outsidesurface, has at least one layer containing at least one heat conductingmetal, at least one layer containing at least one metal with goodthermal conductivity, and at least one second insulating layer. 12.Heating element according to claim 1, wherein the supporting layer,viewed from a free outside surface, has at least one layer containing atleast one metal with good thermal conductivity, at least one layercontaining at least one metal with poor thermal conductivity, and atleast one second insulating layer.
 13. Heating element according toclaim 1, wherein the supporting layer, viewed from a free outsidesurface, has at least one electrically insulating ceramic layer, atleast one electrically conducting ceramic layer and/or at least onesecond insulating layer.
 14. Heating element according to claim 1,wherein the heating element layer is designed as a thick film or as athin film.
 15. Heating element according to claim 14, wherein theheating element layer can be produced by serigraphy or by a printingprocess.
 16. Heating element according to claim 1, wherein the heatingelement layer has a plurality of individual heating resistors which arearranged in at least two heating tracks in such a way that the heatingresistors within each heating track are connected electrically parallelto one another and that the heating tracks are connected in series toone another, and all heating resistors can be supplied simultaneouslywith electrical energy, whereby at least two different heating resistorshave different heating powers and/or the heating resistors are arrangedon the heating element layer at different distances to one another, atleast in regions, and the heating resistors are produced as a thickfilm.
 17. Heating element according to claim 16, wherein the heatingresistors can be produced on the heating element layer with aserigraphic or a printing process.
 18. Heating element according toclaim 16, wherein at least two heating resistors with different heatingpowers have different electrical resistances.
 19. Heating elementaccording to claim 18, wherein at least two of the heating resistorshave different surface areas with different peripheral shapes, differentperipheral lengths, different side lengths, and/or differentthicknesses.
 20. Heating element according to claim 16, wherein theheating power and/or the distance of the heating resistors is adjustedat least in regions based on a pressing strength of the heating elementlayer onto the supporting layer present at least in regions, or to apredetermined heating power density distribution within the heatingelement layer which is present at least in regions, and/or to apredetermined heat density distribution within the supporting layer atleast in regions.
 21. Heating element according to claim 20, wherein theheating power of a first heating resistor which is arranged in a firstregion of the heating element layer with a first pressing strength ofthe heating element layer onto the supporting layer, is smaller than theheating power of at least one second heating resistor, which is arrangedin a second region with a second pressing strength of the heatingelement layer onto the supporting layer, which is smaller in comparisonto the first pressing strength and/or the distance of two heatingresistors to one another is larger in the first region than the distancebetween two heating resistors to one another in the second region. 22.Heating element according to claim 21, wherein the first region islocated near at least one, attachment or pressing location for at leastpartial leadthrough or partial penetration of an attachment device forapplying the heating element layer to the supporting layer, and/or thesecond region is located further removed in comparison to the firstregion from at least one attachment or pressing location.
 23. Heatingelement according to claim 21, wherein the heating power of a thirdheating resistor which is located in a third region of the heatingelement layer with a first heating power density of the heating elementlayer, is smaller than the heating power of at least one fourth heatingresistor which is located in a fourth region with a second heating powerdensity of the heating element layer which is smaller in comparison tothe first heating power density, and/or the distance of two thirdheating resistors in the third region is larger than the distance of twofourth heating resistors in the fourth region.
 24. Heating elementaccording to claim 23 wherein the third region of the heating elementlayer is located near at least one first region of the supporting layerwith a first thermal conductivity and/or with a first heat density andthat the fourth region of the heating element layer is located near atleast one second region of the supporting layer with a second thermalconductivity which is smaller in comparison to the first thermalconductivity and/or with a heat density larger in comparison to thefirst heat density.
 25. Heating element according to claim 16, whereinthe electrical heating resistors of a heating track have essentially thesame heating power, essentially the same geometric dimensions, areessentially at the same distance from one another and/or are madeessentially of the same materials.
 26. Heating element according toclaim 4, wherein the separating layer, the heating element layer, themechanical buffer layer, the first thermal insulating layer, the elasticarresting element and/or the pressing means are designed as one element.27. Heating element according to claim 4, wherein the pressing means,the elastic arresting element, the mechanical buffer layer, the firstthermal insulating layer, the heating element layer and/or theseparating layer can be joined to one another separably or in a fixedmanner.
 28. Heating element according to claim 16, wherein the heatingtracks each have a large number of heating resistors, at least pair-wiseneighboring one another, whereby the heating resistors have a surfacewhich is limited at least partially by first and second side edges,whereby two neighboring heating resistors have facing neighboring firstside edges in order to produce electrical parallel circuits and the twoneighboring heating resistors are at least partially at a distance fromone another and/or are electrically insulated.
 29. Heating elementaccording to claim 28, wherein two facing neighboring second side edgesof the heating resistors of neighboring first and second heating tracks,in order to achieve electrical series connection of the heating tracks,have at least partially at least one first electrically conducting meanslying against the second side edge of the heating resistors of the firstheating track, and against the second side edge of the heating resistorsof the second heating track, and can be connected to one another or areconnected to one another, whereby, using a first electrically conductingmeans, an electric current can be conducted through electrical heatingresistors of neighboring first and second heating tracks.
 30. Heatingelement according to claim 16, wherein at least one second electricallyconducting means connects at least two second side edges of heatingresistors of an outer heating track to one another in a connectingmanner, whereby the at least one second electrically conducting meanshas at least one contact position and/or is in working relationship witha contact position.
 31. Heating element according to claim 30, whereinat least one third electrically conducting means is connected to atleast one first and/or second side edge of a heating resistor of atleast one first outer heating track.
 32. Heating element according toclaim 31, wherein the first, second and/or third electrically conductingmeans comprises at least one electrical material with high conductivity.33. Heating element according to claim 16, wherein at least one set ofneighboring heating tracks are arranged essentially parallel to oneanother and/or at least one heating track is arranged along a straight,curved or circular path.
 34. Heating element according to claim 16,wherein at least two of the heating tracks have different dimensions.35. Heating element according to claim 16, wherein each heating trackhas at least three electrical heating resistors and/or the heatingelement includes at least three heating tracks which can be connected toone another through at least one electrically conducting means and canbe connected electrically to a power source through at least two contactpositions.
 36. Cooking appliance comprising: at least one heatingelement having; at least one supporting layer, at least one heatingelement layer which lies directly or indirectly against the supportinglayer at least in sections, at least one electrical contact orconducting element, and at least one elastic arresting element which isconnected or can be connected to the electrical contact or conductingelement, whereby the electrical contact or conducting element can bebrought into contact using the elastic force of the elastic arrestingelement with at least one heating resistor and/or with at least onecontact location of the heating element layer.
 37. Cooking applianceaccording to claim 36, wherein the at least one heating element can besecured separably on the cooking appliance.
 38. Cooking applianceaccording to claim 36, further including a control and/or regulatingunit which is in working connection with at least one heating elementand/or with at least one electrical heating resistor, and/or with atleast one sensor.
 39. Cooking appliance according to claim 38, whereinthe control and/or regulating unit is capable of operating so that theheating power of the heating element can be controlled and/or regulated.40. Method for the production of a heating element layer of a heatingelement, having a supporting layer, at least one electrical contact orconducting element, and at least one elastic arresting element, which isconnected or can be connected to the electrical contact or conductingelement, whereby the electrical contact or conducting element can bebrought into contact using the elastic force of the elastic arrestingelement with at least one heating resistor and/or with at least onecontact location of the heating element layer, and in which the heatingelement layer lies directly or indirectly against a supporting layer atleast in sections, comprising: preparing a substrate; and applying theheating resistors and/or one or more electrical conducting paths to thesubstrate with a serigraphic technique.
 41. Method according to claim40, wherein a covering layer is subsequently applied to the heatingresistors and/or one or more electrical conducting paths at least inregions.
 42. Method according to claim 40, wherein the substrate isprovided with at least one electrically conducting material, glass,ceramic and/or plastic and/or, before applying the heating resistors,applying at least in regions at least one thermally- and/or electricallyinsulating layer onto the substrate.
 43. Method according to claim 42,wherein the thermally- and/or electrically insulating layer is providedwith at least one ceramic material and/or at least one glass material.44. Method according to claim 41, wherein the covering layer is providedwith an electrically insulating material and/or a material whichprotects against mechanical influences.
 45. Method according to claim40, wherein the heating power, the electrical resistance and/or thedistance of the heating resistors to one another is adjusted bydimensioning the geometric measurements of the heating resistors. 46.(cancelled)